1. Field of the Invention
The invention is in the field of photonic crystals and devices for modulating the frequency of electromagnetic rations.
2. Description of the Related Art
It is a difficult technical problem to create a device that will shift the frequency of electromagnetic radiation with a significant continuous dynamic range. One prior attempt to address the problem has been to use lasers with nonlinear crystals to generate higher harmonics. However, the generated frequencies are at discrete harmonic steps, rather than having a continuous range.
Another attempt to approach the problem has been to use Doppler shifting of frequencies. This produces a continuous shifting of frequencies up or down, but only allows for a limited range of frequency shift. In addition, Doppler shifting does not discriminate in its frequency shifting—all frequencies are shifted by the same amount.
A third way to shift electromagnetic frequency has been to use cavity tuning to shift frequency. However, cavity tuning may be expensive, and in any event produces only a limited amount of frequency shift.
U.S. Pat. No. 6,809,856, to Reed et al., describes a method of modulating frequency of electromagnetic radiation by inputting the radiation into a photonic crystal with a shockwave propagating therethrough. However, the method of propagating a shockwave through a photonic crystal usually destroys the crystal, rendering the method suitable for one-time use only. In addition, the propagating shockwave creates undesirable noise in the radiation output by the photonic crystal.
From the foregoing it may be seen that there is room for improvement in the field of frequency modulation.